<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
    }

    html {
      /* font-size: 16px; */
      /* font-size: 18.35px; */
    }

    header {
      width: 100%;
      height: 4rem;
      font-size: 1rem;
      background-color: lightblue;
      display: flex;
      align-items: center;
      justify-content: center;
    }
  </style>
</head>
<body>
  <div id="app">
    <header>
      腾讯新闻
    </header>
  </div>


  <script>
    // 获取用户的手机宽度
    let width = document.documentElement.clientWidth;

    // html的根字体大小
    document.documentElement.style.fontSize = width * 16 / 375 + "px"
    
    
  </script>
</body>
</html>